From the Guidelines
Miosis, or pupillary constriction, can be caused by various factors including medications, substances, medical conditions, and environmental factors, with common causes including opioids, cholinergic drugs, Horner's syndrome, and bright light exposure. The causes of miosis can be broadly categorized into several groups, including:
- Medications: such as opioids (e.g. morphine, heroin, fentanyl) 1, cholinergic drugs (e.g. pilocarpine, carbachol), and certain antipsychotics
- Substances: like alcohol and nicotine
- Medical conditions: including Horner's syndrome (due to disruption of sympathetic nerve supply), inflammation of the iris, brain hemorrhage (particularly pontine hemorrhage), and neurosyphilis
- Environmental factors: such as bright light, which is a normal physiological response Certain toxins like organophosphates and nerve agents can also cause severe miosis through cholinergic effects 2. Age-related changes can result in smaller pupils as the iris muscles become less responsive. Understanding these causes is crucial for proper diagnosis and management, as restricted pupils can be a sign of serious underlying conditions requiring immediate medical attention, particularly when accompanied by other neurological symptoms. In the context of acute angle-closure glaucoma, miosis can be a significant factor, and treatment may involve medications such as topical beta-adrenergic antagonists, topical alpha2-adrenergic agonists, and topical parasympathomimetics, as well as surgical interventions like laser iridotomy 1.
From the FDA Drug Label
Pilocarpine, in appropriate dosage, can increase secretion by the exocrine glands ... When applied topically to the eye as a single-dose it causes miosis, spasm of accommodation, and may cause a transitory rise in intraocular pressure followed by a more persistent fall The cause of miosis (pupillary constriction) is pilocarpine when applied topically to the eye, due to its muscarinic action as a cholinergic parasympathomimetic agent 3.
From the Research
Causes of Miosis
- There are no direct causes of miosis (pupillary constriction) mentioned in the provided studies 4, 5, 6, 7, 8.
- However, some studies mention conditions that affect the brainstem, such as narcolepsy 4, CLIPPERS (chronic lymphocytic inflammation with pontine perivascular enhancement responsive to steroids) 7, 8, and lesions in the pons 4, 7, 8, which could potentially affect pupillary responses.
- Additionally, one study mentions the use of epidural fentanyl, which can cause nystagmus as a neurological complication 6, but does not specifically discuss miosis.
- Another study discusses the phenomenon of "unconscious pupillometry" and how pupil dilation can be prioritized in visual processing even outside the focus of conscious awareness 5, but does not provide information on the causes of miosis.